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AOA Stall warning
Most AOA systems are really no more than glorified stall warmers. To get the real benefit out of AOA you need an instrument that reads out in degrees AOA. NOW you have a useful instrument. A good AOA instrument will NOT lag and will instantly display the angle between wing chord and relative wind. Now you assign all your V speeds to specific AOA values. Want to depart a short grass strip on a hot day with trees at the end, you can lift off go to 7 degrees AOA (or whatever corresponds to Vx in your airplane) and FORGET the airspeed indicator. Maintain that AOA and the wing will be doing exactly what you need it to do. MUCH better than chasing an airspeed needle with pitch changes while those trees fill the windscreen, and so much more useful than just a stall warner. Unfortunately no one seems to appreciate this aspect of having AOA information in the cockpit.
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Is there a GA AOA system that displays actual degrees?
George |
"Unloading" is just that. Reducing lift by reducing AOA. Sometimes releasing some back pressure is required, sometimes full forward stick is required. Depends on what you are doing. You are unstalling the wing, or getting the wing further from stall AOA.
Airspeed/attitude/angle of bank etc do not matter. You can be wrapped up trying to not overshoot the runway, or at the top of a loop and accidentally got too slow. Reduce AOA to below that of stall, and you are not stalled, and have better control authority. After many decades of unusual attitude training in the 121 world, somebody finally clued in the FAA. The Feds actually have forced standardized upset recovery training on aircrews. The first step, action and callout, is "Push". Navy flight school has taught that for decades, and flying AOA as a performance instrument, not just for stall warning. |
It?s not about AOA or Airspeed; it?s about energy?
90% of what we are doing with the FlyONSPEED project is trying to provide high quality training resources to the EAB community. Lots of these are concepts that we were taught as fighter pilots in the military. Fighter pilots lose control of airplanes too, we just don’t crash very many in the process. Why? Training. The OP reacted just the way he was trained to the stall warning/critical energy cue: unload for control. RV's don't always provide good buffet cues approaching the stall. I first heard the expression "unload for control" as a nugget pilot in the USAF and had to endure regular viewing of a movie by the same name that was part of an Air Force training program for F-4 pilots. One of the young engineers that helped run that flight test and develop those training resources for the USAF was Burt Rutan, fresh out of college.
We’ve put a lot of resources on our web site (www.flyonspeed.org) for anyone that wants to learn more. Under the tab “How to Use the AOA Tone” are four essays that cover the topic in some detail with lots of illustrations and videos. We are always trying to improve those; so any feedback or critique is always welcome. So, from 30K feet…energy management in one picture: ![]() Let’s talk approach and landing first. To land any airplane, you configure, slow to ONSPEED, and maintain ONSPEED until it’s time to flare and touch down. It’s really the old 1.3 Vs you learned in private pilot training, but AOA doesn’t care about G load (bank angle), gross weight or density altitude. This is why it’s such a nifty cue (assuming you have a system that accurately measures AOA, damps the signal and gets the info to the pilot in a usable manner). Any good engineer will tell you that ONSPEED is just an AOA that is a surrogate for a “kinetic parameter” (i.e., airspeed in this case) which is why we’ve been able to come in land for years without an AOA system. What AOA brings to the fight is that it eliminates math…all the pilot does is push or pull (unload or load) the stick to stay in the Goldilocks zone. Warning: “Push” and “pull” are strong terms! That’s why they are lined out in the picture and marked “ease” and “squeeze,” a much better way to think of making those corrections. All US fighter aircraft have used AOA as a primary reference for landing for over 50 years. Oh, and there is some outstanding discussion in this thread: go arounds are free! Silly to die trying to salvage a bad traffic pattern no matter what equipment you have or what your experience is. Again, training and mindset are the key--far more important than equipment. Now let’s talk maneuvering flight, because it’s some of the most fun we have with our clothes on…Refer to picture one above. Don’t pull any harder than ONSPEED when maneuvering. Why? In simple terms, when the airplane is ONSPEED, energy is “neutral” (thrust and drag are balanced for a given power setting, including full throttle). If you pull any harder (get a slow tone in our example), energy is “negative,” i.e., you’ve got more drag than thrust. That means you are going down, slowing down or both in that condition. To maintain aircraft control means more than just not stalling, it means having sufficient energy to maneuver as well. Here’s a video that I recently posted over on the Safety Page that has a good, constant AOA maneuvering set in it (along with some other maneuvers that illustrate AOA in action). You need to crank the volume to hear the tone clearly. The tone is low because I had it turned down to normal levels (I usually crank it up for videos so it comes through loud and clear). This was a flight test and wasn’t intended as a training video—it just illustrates the key concepts in this post in six minutes or less: https://youtu.be/Hav7LMIeBFo. Remember how we learned that an airplane can stall in any attitude and at any airspeed? The accelerated stall occurred at 5.1 G’s and the airspeed is right around maneuvering speed (132 MPH IAS ish on the stand-by ASI visible in the video). Also listen to the instances of slow tone, even with my nose and lift pointed down at the same time. To summarize, all of the above in three words or less: “unload for control" :) Yes, you can accurately measure absolute angle of attack (the difference between zero lift and the chord line of the wing) with a coefficient of pressure system to with a 1/4-1/2 of a degree and have that system provide a damped cue at high G onset rates (that’s just a fancy way of saying it works in turbulence or if you pull on the stick hard). Turns out all you need are some great test airplanes (RV’s), good engineers with a sense of humor, 100LL, patience and great community support from the VAF family to do that. Last item: any AOA system can be helpful, even if all it does is provide progressive stall warning. It needs to be properly calibrated and you need to understand how it works in an operational environment. Keep in mind that AOA systems are like a pitot/static system, i.e., calibration dependent and unless you have an identical, tested calibrations, take any specifics you hear (or read online) with a grain of salt since there is variation from airplane to airplane (i.e., just like you can’t directly compare IAS). This is why we are experimenting with automating the AOA calibration to make sure that an orange is an orange—remains to be seen if we’ll be able to pull that off; but it won’t be for a lack of trying! v/r, Vac |
GRT synthetic AOA
Vac, great info, as usual. Have you or any of your comrades had any experience with the GRT synthetic AOA? Paul Dye seemed to feel it was pretty good for pattern/landing back in the day, but not sure if that view still holds. If it's good, I can remove 3 or 4 ounces of plastic tubing. :D
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Unloaded = 1G (Some may argue 0G is unloaded. OK. However 0G is not relevant to normal motoring around the sky, more aerobatics. I do aerobatics and never am at 0G doing my normal +G routine except momentarily. Bottom line AOA and stall is relevant to G loading and 1G is the bench mark for stall speed.)
AOA vane (like a weather vane) is actual angle of attack. The ones Garmin and Dynon and GRT use are differential air-pressure and is "derived" AOA (an estimate). There are AOA indicators (derived) that do not use either vane or pressure. It uses airspeed, pitch, G's, VSI and software to estimate margin to critical angle of attack... Call it electronic seat of the pants. On Jets besides the AOA they have a Flight Data Computer that takes in all parameters and limits and warns the pilot. Although no direct visual AOA bars are shown may see a stall limit indication on airspeed tape and stick shaker.... among other warnings. For most flying GA or commercial we don't work close to stall (except right before touchdown) but AOA indicator is a powerful tool. However if your RV has no AOA we know the stall speed of our aircraft "unloaded", giving you a margin of safety to stall. |
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What Vac said...
I have been flying with his Gen 1 tone generator for nearly 2 years now and I freaking love the thing...
Have used heads-up display in USAF (indexer) and AOA gauge (also USAF and Part 121), so I am familiar and have flown with some of the mentioned systems. I like the tone soooooo much better. Immediate feedback loop on what the wing is doing with no “eye distraction/heads down” inside to look at indexers, gauges, etc. Intuitive. Easily learned. Valuable feedback not only in pattern work, but in maneuvering flight as well. Also, I learned that most of the speeds I was using in the pattern were too fast...I find my touchdown points more accurate and landings more consistent when flown using the tone vs a straight airspeed reference. For example, in the OP’s case had he been flying with Vac’s system, he would have been getting AOA trend info all the way as he slowed on downwind, around the final turn, and not just an alert when getting slow on the overshoot. In any case, if flying the On Speed tone won’t give you a safe final turn without an overshoot, you’ll know to take it around early enough to not be hazardous. Takes a few flights to get used to, but am totally addicted and would not be as comfortable now without it. EAA Innovation Award winner year before last...great system Vac! Rob |
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Larry |
my AOA helps in other ways too
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My AOA- a Lift model Aircraft & Spruce P/N 05-14964 is a gauge with no aural warning. I look at it during my "normal carrier type approaches" and confirm my margin above stall. The additional benefit is that I have reduced my grass landings to ~500-550ft no brakes needed when flying the AOA. Really think it was worth $312 for the added safety. Also use it during engine out practice. Safe flying Daddyman |
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